The Construction Of Bio-based Flame Retardants Based On Tannic Acid And Their Application In Polylactic Acid

As an environmentally friendly polymer,polylactic acid(PLA)can reduce the negative impact of non-degradable petroleum-based polymers on the environment.However,it suffers from the drawbacks like flammability,UV sensitivity,and slow natural degradation,severely limiting its application.This paper designed bio-based flame retardant systems around tannic acid(TA)and blended them with PLA to prepare multifunctional biodegradable composites.And the flame retardant mechanism,anti-UV aging mechanism,and biodegradation mechanism of the composites were studied to consider the life cycle of PLA products to a greater extent.The main contents of the three chapters for this topic are as following:(1)LC-PA was synthesized from citrulline(LC)and phytic acid(PA)via Mannich reaction and then blended with TA to introduce into PLA.The PLA composite containing 10%LC-PA/TA achieved an LOI value of 26.9 and a V-0rating in the UL-94 test;the maximum heat release rate and total heat release of the sample were reduced by 24.4%and 21.1%,respectively.After soil burial degradation,the PLA/10%LC-PA/TA sample showed a significant decrease in molecular weight with the change ratios of M_n,M_w,and M_zof31.2%,31.4%,and 51.2%,significantly higher than pure PLA(14.8%,16.0%,23.3%).(2)The trinity flame retardant(BA-TA-MEL)was prepared by Boric acid(BA),melamine(MEL),and TA through ionic complexation reaction before being blended with PLA.The PLA/5%BA-TA-MEL composite increased LOI value to 27.1 and passed a V-0 rating in the UL-94 test with the droplets reducing.The mechanical properties of PLA/5%BA-TA-MEL could remain at a high level after 100 h of UV irradiation,and its UV protection factor(UPF)increased from 0.4 of PLA to 290.4.In addition,BA-TA-MEL acted as rigid organic particles in the matrix,which increased the tensile strength of PLA composites from 51.5 MPa for pure PLA to 61.4 MPa.(3)Based on the research in the first two chapters,the third chapter was expected to synthesize integrated additives to simultaneously endow the flame retardancy,UV resistance capability,and the fast degradation rate of PLA.Specifically,PA@TA-CS was prepared by synthesizing TA-CS via radical grafting reaction between chitosan(CS)and TA,then encapsulating PA on the surface through electrostatic adsorption.3%PA@TA-CS can reduce the maximum temperature of PLA melt droplets by 44.8%in the UL-94 test without igniting absorbent cotton.The PLA/3%PA@TA-CS sample can block99%of UV light transmission,and its UPF value was as high as 852.2.Degradation tests showed that PA@TA-CS significantly accelerated the hydrolysis rate of the PLA matrix and promoted the formation of microbial films on the surface of the sample.After soil burial,the M_nand M_wretention ratios of PLA/3%PA@TA-CS were 71.4%and 76.2%,respectively,much lower than PLA.